Contextuality, a
far-reaching generalization of nonlocality, stands out as a necessary
resource for fault-tolerant quantum computation and other
quantum-information tasks. Still, contextuality itself is not a
signature of quantumness, since it can be simulated by classical
models at the cost of extra memory. So far, these models are created
ad hoc for each contextuality proof. This raises the question of
whether quantum contextuality can be universally simulated with
classical systems. Here we show [1] that classical electromagnetic
waves provide a universal model for quantum contextuality in
experiments with sequential measurements in which intermediate
outcomes are stored in extra degrees of freedom. We support this by
presenting experimental evidence of the state-independent violation
of the Peres-Mermin noncontextuality inequality and the
state-dependent violation of the noncontextuality version of Mermin's
inequality with classical microwaves at the frequency used in
consumer ovens. This is based upon the detection of intensity
correlations under the assumption that intensities are ultimately due
to a succession of individual events. Our results coincide with those
found in quantum tests with ions, photons and neutrons. Unlike ad hoc
classical contextual models, classical electromagnetism emerges as a
universal model revealing the precise location of the memory needed
to generate contextual outcomes and the mechanism to do it: the
relative phase of the electromagnetic field in the extra degrees of
freedom storing the intermediate outcomes. The principles explaining
the bounded nature of contextuality and nonlocality in quantum theory
are then tied to the question of why classical electromagnetism,
under proper tests, is equally bounded.